(a). Technical Field of the Invention
The present invention relates generally to actuator technology. More particularly, it relates to an apparatus and method for latching an actuator using thermally reactive shape-memory wires.
(b). Description of Related Art
Current actuators are based primarily on electromagnetics. These actuators convert electrical energy into magnetic energy which is then converted into mechanical energy. The most common types of these actuators are the rocker, the latching solenoid, and the rotary magnet.
In the rocker and the latching solenoids, electric current is passed through a wire coil at one end of an actuator to create a magnetic field. The magnetic field pulls a soft iron rocker (or armature) towards the wire coil. Once in position at the end of the actuator, the soft iron rocker serves as an electrical connection between two terminals. A permanent magnet near the wire coil at the end of the actuator secures the soft iron rocker in position even when the electric current is removed from the wire coil.
When it is desired to open the circuit between the two terminals, an electric current is passed through a second wire coil located on the opposite end of the actuator. This creates a magnetic field that overcomes the magnetic force of the permanent magnet and attracts the rocker toward the other side of the actuator. As the rocker breaks contact with the two terminals, the electrical connection between the terminals is removed. A second permanent magnet is typically used to help secure the rocker near the second wire coil. These actuators require a soft iron moving piece, one or two permanent magnets to provide latching force, two coils, and soft iron pole pieces.
The rotary magnet actuator has two permanent magnets attached to opposite ends of a rotating lever. The permanent magnets are positioned on the lever such that the polarity of one magnet is opposite of the other. A movable permanent magnet is positioned below the rotating lever and provides the mechanical actuating force for the circuit. When it is desired to actuate the circuit, the lever is rotated to bring one of the permanent magnets near the movable magnet. Depending on the polarity of the closest permanent magnet, the movable magnet will either be attracted or repelled. This magnetic force will drive the movable magnet to one end of the rotating actuator. To move the magnet to the other end of the actuator, the lever is rotated to bring the opposite permanent magnet near the movable magnet. This type of actuator requires a moving magnet, a lever, permanent magnets for the disk, and an actuating device to provide rotary motion to the level, which is typically an electromagnetic actuator consisting of a magnet, coils, bearings, and soft iron laminations.
The above-described actuators are relatively bulky, complex, and require a relatively large number of components. Accordingly, these actuators are not well suited for use where space and weight is at a premium, such as spaceships and satellites. There is, therefore, a need for an actuator that is small and light weight, and, therefore, useful in applications such as spaceships and satellites.